PROJECT SUMMARY/ABSTRACT Vocal communication plays a pivotal role in shaping the dynamics of social interactions and is impaired in a wide range of neurological disorders. Consequently, a major component of translational research focuses on identifying circuit-level neurobiological mechanisms underlying social communication deficits. Determining the neural mechanisms underlying social communication deficits requires both understanding the functions of neural circuits as well as the ability to link neural circuits to specific naturalistic behaviors. However, obtaining this information has been challenging because of the difficulties in interpreting complex behavioral interactions in freely socializing animals. The long-term goal of this research is to understand the neural circuitry controlling naturalistic social behaviors directly influenced by communication. This could ultimately allow communication disorders to be treated by therapeutically targeting atypically functioning neural circuitry. In pursuit of this goal, the overall objective in this proposal is to determine how social communication is encoded in the nervous system and the role it plays in shaping behavior. The proposal uses a novel microphone array system to track the vocal behavior of freely socializing, individual adult mice?a technique that has eluded the field for 50 years. Coupling this innovative method with in vivo wireless electrophysiology and machine-learning techniques used for robustly extracting meaningful social information will enable identification of the neural circuits that encode social communication and the role communication plays in directly shaping social behavior. Aim 1 will test the hypothesis that mice emit behavior-dependent vocalizations that directly alter the social dynamics between animals. Aim 2 will test the hypothesis that behaviorally-dependent vocalizations are encoded in the CA2 subregion of the hippocampus. Aim 3 will test the hypothesis that the lateral entorhinal cortex, one of the primary cortical inputs to CA2, encodes the locations of vocalizations in egocentric reference frames. The proposed research will have a broad impact as these studies will provide fundamental insight into the neurobiological basis of social communication. Moreover, these experiments will lay the groundwork for future studies examining the neural basis of social communication in mouse models of neurological disorders, such as schizophrenia, Parkinson?s disease, and autism spectrum disorders.